1. Field of the Invention
The present invention relates to image forming apparatuses such as a copying machine, a printer and a facsimile.
2. Description of the Prior Art
Examples of a copying machine already developed include one in which an electrode composed of a metal revolving roller is provided on the downstream side of a developing device in the direction of rotation of a developing roller, a bias voltage is applied to the electrode to generate an electric field between the developing roller and the electrode, toner particles are supplied to a photosensitive drum and then, toner particles remaining on the surface of the developing roller and floating toner particles are attracted to the electrode to prevent the occurrence of nonuniformity of an image and fogging (see Japanese Utility Model Laid-Open Gazette No. 57763/1989).
The above described conventional copying machine has the following disadvantages:
(a) A power supply for applying the bias voltage to the electrode is required, thereby increasing cost.
(b) A terminal such as a brush must be used so as to supply the voltage to the electrode composed of the metal revolving roller, so that the bias is liable to be unstable and the terminal must be periodically replaced.
(c) In cases, for example, immediately after the copying machine is stopped, when the power supply of the copying machine is turned off immediately after copying is terminated, and when a front door of the copying machine is opened by paper jamming or the like, the electrode is not biased, so that the floating toner particles cannot be attracted to the electrode.
(d) Since the electrode composed of the metal revolving roller has high thermal conductivity, dew condensation is brought about on the surface of the electrode composed of the metal revolving roller if the temperature is changed at the time of, for example, the replacement, so that the toner particles adhering to the electrode are melted and the melted toner particles are recovered by the developing device, thereby exerting adverse effects on the toner particles.